As a heating value of a semiconductor element is increased, there are a number of examples where a water-cooling type cooling device is adapted instead of an air-cooling type cooling device such as a heat sink.
FIG. 13 is a view showing an example of the water-cooling type cooling device.
With reference to FIG. 13, a cooling device 400 is to cool a semiconductor element 406. Cooling water fed from a pump 402 to a heat absorbing unit 404 is injected from an injection port 408 to the inside of a part where the semiconductor element 406 is installed so that cooling efficiency is enhanced. In such a way, there is a well-known technique that thermal transmission is facilitated in a form of a wall-surface colliding jet.
FIG. 14 is a view showing an example of a cooling device with using a conventional wall-surface colliding jet.
The cooling device as shown in FIG. 14 is disclosed in Japanese Patent Laying-Open No. 2001-135763. With reference to FIG. 14, a semiconductor element 501 is sealed by a ceramic cap or the like and connected to a ceramic substrate 502 by a very small solder ball 503. The electric power is supplied to and a signal is inputted to and outputted from semiconductor element 501 via a pad 504 connected to solder ball 503 by a wire (now shown) provided in the interior of the substrate.
A support body 507 has an opening unit 525 for housing semiconductor element 501 and supports or retains ceramic substrate 502. A pin 509 is partly provided on a surface of the support body so as to position ceramic substrate 502 relative to the support body. A spacer 508 is to feed the air between ceramic substrate 502 and support body 507.
A gap 511 is a gap between semiconductor element 501 and opening unit 525 on an upper surface of support body 507. A gap 512 is a gap between ceramic substrate 502 and support body 507 generated by spacer 508. A discharge port 514 is a discharge port for a coolant and the air provided in a casing 513.
When an electric characteristic of semiconductor element 501 is measured and evaluated or devices are divided into a non-defective item and a defective item, semiconductor element 501 is firstly set downward so as to form gap 511 relative to support body 507 in opening unit 525 for housing semiconductor element 501.
Then, the air in casing 513 is drawn out by a blower 517 and the air is taken from the upper side of support body 507 into casing 513 via gaps 512 and 511.
Next, while continuously taking the air in such a way, cooling water of a tank 516 is cooled by a heat exchanger 518 and further injected from a coolant injection nozzle 510 toward a main surface of semiconductor element 501 (a surface of the ceramic cap) by a pump 515. An arrow 519 indicates flow of the air to be suctioned into gaps 511 and 512. An arrow 520 indicates flow of the cooling water. Pump 515 for the coolant also suctions the cooling water and the air from discharge port 514. Then, the air and the water are separated from each other in tank 516.
When the air is discharged from discharge port 514 provided in casing 513 on the lower side of support body 507 to tank 516 by blower 517, the air at a normal temperature is fed from the periphery of the cooling device of FIG. 14 into gap 512 between ceramic substrate 502 and support body 507 and gap 511 between support body 507 and a side surface of semiconductor element 501. An air curtain 521 is formed around semiconductor element 501. Flow of the cooling water injected to the main surface of semiconductor element 501 and the like are pushed away to the downstream by this air curtain 521.
Since a jet is injected to such a wall surface in the gas, the speed of the jet is not weakened in comparison to injection in the liquid and heat radiation efficiency from the semiconductor element is improved.
Vehicles using the electric power as a mechanical power source such as a hybrid vehicle, an electric vehicle and a fuel-cell vehicle provided with a fuel cell attract public attention in recent years. The hybrid vehicle is a vehicle having a motor as the mechanical power source in addition to a conventional engine. The hybrid vehicle is to obtain the mechanical power by driving the engine and converting DC voltage from a DC power source into AC voltage so as to drive the motor by the converted AC voltage. The electric vehicle is to obtain the mechanical power by driving a motor by AC voltage converted from DC voltage from a DC power source.
An electric power transducer such as an inverter and a voltage boosting converter is installed in such a vehicle using the electricity as the mechanical power source. The electric power transducer to be installed in the vehicle or the like requires a large volume of the electric power in order to obtain a high mechanical performance. Since the electric power transducer with a large volume of the electric power or the like generates a large heating value, a cooling device for cooling the electric power transducer is installed.
The electric power transducer includes a plurality of power semiconductor elements. For example, the power semiconductor elements include power MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).
With regard to such a cooling device for cooling the semiconductor element to be installed in the vehicle, it is worth while examining facilitation of the thermal transmission in the form of the wall-surface colliding jet in order to improve the cooling efficiency.
However, in the example as shown in FIG. 13, when the semiconductor element to be cooled is increased to more than one, the semiconductor element installed on the downstream side of the cooling water is influenced by the cooling water injected to the other semiconductor element on the upstream side. Therefore, the cooling water is not easily injected to each of a plurality of the semiconductor elements at a uniform flow rate, and there is a fear that cooling unevenness may be caused.
The form of the wall-surface colliding jet of an open system where a casing communicates with the external air as shown in FIG. 14 is not preferable as the cooling device to be installed in the vehicle where oscillation and acceleration are added, since there is a fear that leakage of the cooling water may be caused.